Does the synthesizer have any special layout considerations?
For synthesizers requiring external inductances, refer to Application Note 31 – Inductor Design for the Si41xx Synthesizer Family for details on how to implement the external inductors. A rule of thumb is to use discrete inductors if the required external inductance is greater than 3 nH.
Inductance values for chip inductors progress in discrete steps. To implement specific inductances therefore, a combination of both PCB and trace inductances may be required.
Precautions should be taken to isolate the reference frequency input trace, the RF output traces, and the inductor traces from potential sources of interference or coupling. The Si4133/33G-EVB datasheet contains layouts for various evaluation boards.
Good grounding techniques should be employed to minimize unwanted signal coupling. This involves ensuring that each RF signal has a continuous ground return path back to its source. The return path should closely follow the sourcing signal’s trace. For MLP packages, connect the ground paddle located in the center of the package to PCB ground. The VDD supply of the synthesizer should be locally bypassed as close to the part as possible. Refer to the “Typical Applications Circuit” diagram in the synthesizer device datasheet for the recommended bypass capacitance.
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